Oncogenes—genes that contribute to the production of cancers—are generally mutated forms of certain normal cellular genes (“proto-oncogenes”). Oncogenes often encode abnormal versions of signal pathway components, such as receptor tyrosine kinases, serine-threonine kinases, or downstream signaling molecules. The central downstream signaling molecules are the Ras proteins, which are anchored on the inner surfaces of cytoplasmic membranes, and which hydrolyze bound guanosine triphosphate (GTP) to guanosine diphosphate (GDP). When activated by a growth factor, growth factor receptors initiate a chain of reactions that leads to the activation of guanine nucleotide exchange activity on Ras. Ras alternates between an active “on” state with a bound GTP (hereafter “Ras.GTP”) and an inactive “off state with a bound GDP. The active “on” state, Ras.GTP, binds to and activates proteins that control the growth and differentiation of cells.
For example, in the “mitogen-activated protein kinase (MAP kinase) cascade,” Ras.GTP leads to the activation of a cascade of serine/threonine kinases. One of several groups of kinases known to require a Ras.GTP for their own activation is the Raf family. The Raf proteins activate “MEK1” and “MEK2,” abbreviations for mitogen-activated ERK-activating kinases (where ERK is extracellular signal-regulated protein kinase, another designation for MAPK). MEK1 and MEK2 are dual-function serine/threonine and tyrosine protein kinases and are also known as MAP kinase kinases. Thus, Ras.GTP activates Raf, which activates MEK1 and MEK2, which activate MAP kinase (MAPK). Activation of MAP kinase by mitogens appears to be essential for proliferation, and constitutive activation of this kinase is sufficient to induce cellular transformation. Blockade of downstream Ras signaling, as by use of a dominant negative Raf-1 protein, can completely inhibit mitogenesis, whether induced from cell surface receptors or from oncogenic Ras mutants.
The interaction of Raf and Ras is a key regulatory step in the control of cell proliferation. To date, no substrates of MEK other than MAPK have been identified; however, recent reports indicate that MEK may also be activated by other upstream signal proteins such as MEK kinase or MEKK1 and PKC. Activated MAPK translocates and accumulates in the nucleus, where it can phosphorylate and activate transcription factors such as Elk-1 and Sap1a, leading to the enhanced expression of genes such as that for c-fos.
Once activated, Raf and other kinases phosphorylate MEK on two neighboring serine residues, S218 and S222 in the case of MEK1. These phosphorylations are required for activation of MEK as a kinase. In turn, MEK phosphorylates MAP kinase on two residues separated by a single amino acid: a tyrosine, Y185 and a threonine, T183. MEK appears to associate strongly with MAP kinase prior to phosphorylating it, suggesting that phosphorylation of MAP kinase by MEK may require a prior strong interaction between the two proteins. Two factors—MEK's unusual specificity and its requirement for a strong interaction with MAP kinase prior to phosphorylation—suggest that MEK's mechanism of action may differ sufficiently from the mechanisms of other protein kinases as to allow for selective inhibitors of MEK. Possibly, such inhibitors would operate through allosteric mechanisms rather than through the more usual mechanism involving blockage of an ATP binding site.
Thus, MEK1 and MEK2 are validated and accepted targets for anti-proliferative therapies, even when the oncogenic mutation does not affect MEK structure or expression. See, e.g., U.S. Patent Publications 2003/0149015 by Barrett et al. and 2004/0029898 by Boyle et al.
Several examples of 1-substituted-2(p-substituted-phenylamino)-aryl inhibitors of MEK have been reported. U.S. Pat. Nos. 6,440,966 and 6,750,217 and corresponding publication WO 00/42003 described carboxylic and hydroxamic acid esters and N-substituted amide derivatives of sulfonamide-substituted-2(4-iodophenylamino)-benzoic acid esters and N-substituted benzamides as functioning as MEK inhibitors. The sulfonamide may also be N-substituted.
U.S. Pat. No. 6,545,030 and corresponding publication WO 00/42029 describe MEK inhibitors that are 1-heterocyclyl-2(4-iodophenylamino)-benzene, where the heterocycle is a five-membered nitrogen-containing ring such as pyrazole, triazole, oxazole, isoxazole, and isoxazolinone. The more recent U.S. Patent Publication 2005/004186 describes related compounds in which the 4-iodo substituent of the '030 patent is replaced by a very broad genus of moieties including alkyl, alkoxy, acyloxy, alkenyl, carbamoyl, carbamoylalkyl, carboxyl, carboxylalkyl, N-acylsulfonamido, and others.
U.S. Pat. No. 6,469,004 and corresponding publication WO 00/42022 describe carboxylic and hydroxamic acid esters of a group of heterocyclo-condensed phenylene compounds, i.e., benzimidazoles, benzooxazoles, benzothiazoles, benzothiadiazoles, quinazolines, etc. The heterocycles are 7-F-6-(4-iodo-phenylamino)-5-carboxylic acid esters, carboxylic acid amides or hydroxamic acid esters. More recent publication U.S. 2005/0026970 described similar compounds in which the 4-iodo substituent was replaced by a very broad genus of structures. Related compounds are described in patent publications WO 03/077855, WO 03/77914 and US 2005/0554701. Further examples of 2-(4-iodophenylamino)-phenylhydroxamic acid esters which are reported to be useful as MEK inhibitors can be found in WO 2005/028426. Patent Publication WO 02/06213 and corresponding U.S. application Ser. No. 10/333,399 (U.S. 2004/0054172) describe hydroxy-substituted acid esters of 1-oxamic acid-2(4-halophenylamino)-3,4-difluorobenzene. U.S. Pat. No. 6,891,066 and corresponding publication WO 03/62191 describe similar compounds wherein the 4-halo substituent is replaced by a very broad genus of structures. Among the substituents in the 4-position were methyl, ethyl, ethynyl, and 2-hydroxyethyl. Specific related compounds are described in U.S. Pat. No. 6,770,778.
Patent Publication WO 04/083167, published Sep. 30, 2004, (in Japanese) discloses more than two thousand—but provides NMR data for only 400—1-(N-substituted sulfonyl urea)-2(2,4-dihalophenylamino)-3,4-difluorobenzenes and asserts that they useful as MEK inhibitors. Data indicating inhibition of MEK were presented for a subgroup of just twelve. In addition to a secondary or tertiary amine, these twelve compounds all contained one of the following groups: an N,N-disubstituted sulfonyl urea, N-piperazinesulfonamide, N-piperidinesulfonamide or N-pyrrolidinesulfonamide.
The MEK cascade has also been implicated in inflammatory diseases and disorders. U.S. Application Publication No. 2006/0030610 to Koch et al., U.S. Application Publication No. 2006/0140872 to Furue et al. This includes both acute and chronic inflammation disorders. Examples of such disorders are allergic contact dermatitis, rheumatoid arthritis, osteoarthritis, inflammatory bowel diseases, chronic obstructive pulmonary disorder, psoriasis, multiple sclerosis, asthma, diseases and disorders related to diabetic complications, and inflammatory complications of the cardiovascular system such as acute coronary syndrome. Among inflammatory bowel diseases are Crohn's disease and ulcerative colitis.
All cited references are incorporated herein by reference.